The field of the present invention is control and stabilization of an automotive vehicle. More particularly, the invention relates to structure and methods for effecting control and stabilization of an airborne automotive vehicle such as a rocket or guided missle.
Because such a vehicle is generally designed to fly at relatively high speeds, the aerodynamic control surfaces of the vehicle are relatively small in the interest of minimizing drag within a design flight speed range for the vehicle. Although the aerodynamic control surfaces are effective at design flight speeds, and generally are also effective at lesser speeds exceeding a control threshold speed, they cannot provide sufficient aerodynamic control force below the threshold speed to insure control and stabilization of the vehicle.
Consequently, a control and stabilization problem arises in launching such a vehicle from rest or from a low-speed launch vehicle. For example, missiles launched from rest on the earth, from a ship at sea, or from a low-speed aircraft such as a helicopter, may encounter stabilization and control deficiency due to a low launch velocity.
One solution to the problem is to provide a booster rocket engine supplying sufficient impluse to the vehicle that the latter attains or closely approaches the control threshold speed before leaving its launch guide rail or tube. However, this solution exposes structure and personnel close to the launch site to blast, heat, and concussion from the booster rocket engine. A person exposed to such effects may be injured or killed. Aboard ship, structure such as radar antennae and optical sighting devices may be damaged by such blast effects unless special precautions are taken. In the case of missile launches from slow-speed aircraft, and helicopters in particular, it has been discovered that the blast from the booster rocket engine pits and otherwise deteriorates the aircraft windshield so badly that the windshield must be repaired or replaced after only a few missile firings. In view of the above, it is easy to appreciate the plight of a soldier who must fire a shoulder-launched anti-tank or anti-aircraft missile. If the soldier is in a relatively confined area which prevents dissipation of the blast at the time of missile firing, such as a narrow alley or doorway, he may be injured or killed by the launching blast of his own weapon.
As a consequence, it has proposed to employ a "soft launch" technique wherein a booster rocket engine with a relatively small ejection grain is used to pop the missile from its launch rail or tube and lob it in the direction of the target. The ejection grain of the rocket booster engine would cause very little blast or concussion. After the ejection grain burns out, the main booster grain of the engine is ignited and accelerates the missile to its design flight speed range. However, by the time the main booster grain is ignited, the missile is sufficiently spaced away from its launcher that the resulting blast and concussion do no damage.
Unfortunately, a "soft launch" technique exacerbates the problem of stabilization and control of the missile prior to its attaining its control threshold speed. That is, the missile may wander off course or even start to tumble while it is being lobbed away from its launcher. Of course, if the missile deviates too far from its intended course, recovery may not be possible during the very rapid acceleration caused by ignition of the main booster grain. The missile may accelerate off course, into the earth, or even toward its own launcher.
U.S. Pat. No. 3,276,376, granted Oct. 4, 1966, to R.W. Cubbison, et al., teaches one apparatus and method which it is believed could be used to stabilize a missile during a soft launch. According to the teaching of Cubbison, a missile includes aerodynamic canard control fins each of which also defines a penshaped external-expansion nozzle. Each fin-nozzle is associated with a respective combustion chamber within the missile which delivers combustion products to the nozzle. During low-speed flight of the missile the combustion chambers are operated and pivoting of the fins serves to direct or vector the resultant thrust to effect control of the missile.
However, the Teaching of Cubbison is believed to have many deficiencies. For example, the canard fins, are exposed directly to very hot combustion products so that they must be fabricated of heat resistant material. Further, because of pivoting of the canard fins, fuel and oxidizer must be communicated to the combustion chambers through flexible conduits. Such flexible conduits may be failure prone. Further, the Cubbison teaching utilizes penshaped external expansion nozzles rather than the more conventional and more efficient convergent-divergent nozzle design.